The present invention relates to hydraulic jarring tools and more particularly to an apparatus for delivering an impact for freeing objects which may be lodged in an oil well or the like to free the same and permit recovery.
During drilling operations, such as are conducted in the oil industry, drill pipe or other objects occasionally become lodged in the drill hole. the lodging may result from a variety of causes, such as cave-ins, or the like but regardless of the cause, the lodging of the equipment presents problems. If the object is sufficiently lodged so that the equipment can be neither turned nor withdrawn by ordinary movement of the drill pipe, the well drilling operation will be impaired.
The equipment which has been developed for removing such lodged objects is commonly referred to as "fishing" equipment and has taken many forms over the years. A common form of "fishing" equipment is a hydraulic jarring device which is located at the lower region of a string of drill pipe. In known hydraulic jarring tools, the impediment mechanism which impedes movement of hydraulic fluid in the jarring tool is placed under the intense pressures generated by the surface-mounted hoisting apparatus. These known devices have not been totally satisfactory because the intensity or magnitude of the tension placed on the jarring tool often varies while the tool is being used. The metering arrangements used in known devices are such that, when the magnitude of the pull is changed, so too does the intensity of the pressures generated in the tool. Such varying pressures may result in undesirable variations in the magnitude of the jarring force applied to the fish.
Certain prior art devices utilized to free objects lodged in wells incorporate a mechanism for compressing a fluid within the tool, and then suddenly releasing that pressure to enable impact surfaces of the tool to engage and produce an impact which is transmitted to the lodged object. These prior art devices are generally complex and are designed in such a manner that the fluid, which is under intense pressure, is transferred or metered to control the movement of the mandrel. These known devices employ various mechanisms for regulating the flow of the fluid, and also frequently employ specific fluids to combat problems caused by the pressures and temperatures encountered in deep bore holes.
Most known deep well hydraulic jarring tools employ metal to metal seals between a jarring barrel and a distensible sleeve for controlling the telescoping movement of the jar. The shape of such barrels often becomes slightly eliptical, or otherwise distorted, and frequently produces unreliable operation. This distortion could result from using drill pipe tongs at well sites to tighten or loosen threaded sections. Furthermore, such distensible sleeves tend to leak under the intense pressures generated in a jarring operation and often become worn due to frictional engagement with other jar tool parts as they are pulled up the case prior to the tripping of the jarring device.
One known device is shown in U.S. Pat. No. 3,729,058 issued to Roberts on Apr. 24, 1973. This device utilizes axially spaced, sliding seals between the mandrel and the barrel to maintain a continuous fluid seal as the mandrel and barrel are moved axially relative to one another. During upward movement of the mandrel, pressure generated above an upwardly moving sleeve increases, causing a thin-wall section of the sleeve to distend radially outward and into sealing engagement with the wall of a compression chamber. Movement of the sleeve is impeded until a trip point is reached. See also, U.S. Pat. Nos. 3,566,981 and 3,429,389.
A further drawback of many known jarring tools is that impact is developed while resetting the tool. This could result in further lodging a fish, or increasing the time and number of strokes necessary to dislodge the tool.
Another drawback of known jarring devices is that the resetting operation requires a relatively long time. Obviously, since the resetting of the device accomplishes no useful work, the time needed to reset should be minimized.
The mechanism of the present invention overcomes the above-discussed drawbacks, as well as others, by providing a jarring device incorporating a simple, yet effective, movement impediment mechanism which is controlled by a metering system whose operation varies depending upon the load developed by the hoisting apparatus.